Nanorods gain gold tips

Researchers from Hebrew University in Israel
have devised a way to cause semiconductor nanocrystals and tiny amounts
of gold to self-assemble into nanoscale dumbbells, chains and tetrapods.

The rods and tetrapods could eventually serve as ultra-small transistors,
memory elements, light-emitting elements and sensors in nanoelectronic
and optoelectronic circuitry, according to the researchers. The researchers'
semiconductor-gold dumbbells, chain links and tetrapods range from 20
to 40 nanometers in length. A nanometer is one millionth of a millimeter,
or the size of a row of 10 hydrogen atoms.

The ability to grow gold tips on nanoscale bits of semiconductor
is a significant step toward solving the difficult manufacturing problem
of how to wire such small objects together.

The gold tips are bonded to the semiconductor covalently, meaning
the gold and semiconductor atoms share one or more electrons; this provides
a good electrical contact. The gold provides natural anchor points for
connecting semiconductors to electrodes and for self-assembly.

The chemical process the researchers used to bind the gold tips
to the semiconductors was fairly simple and straightforward, according
to the researchers. This concept could be used to fuse nanorods to other
metals, including those that are magnetic.

The nanorod-gold objects could also lead to materials with new
chemical and optical properties, according to the researchers.

Use of the gold-tipped metal structures in novel self-assembly
could happen within five years; practical applications in nanoelectronics
and optoelectronics will emerge in five to ten years, according to the
researchers. The work appeared in the June 18, 2004 issue of Science.